COAL  IN  SANPETE  COUNTY,  UTAH. 
By  G.  B.  Richardson. 
INTRODUCTION. 
The  report  of  the  State  mine  inspector  for  1904  credits  Sanpete  County  with  a  produc- 
tion of  6,033  tons  of  coal,  out  of  1,563,274  tons  mined  in  I 'tali.  This  small  amount  is  fur- 
nished by  two  mines  oik-  near  Wales,  which  supplied  only  400  tons,  and  the  other  near  Ster- 
ling. Though  the  production  of  Sanpete  County  is  small,  the  occurrence  of  coal  there  is 
perhaps  <>f  more  than  local  interest.  Wales  claims  the  distinction  of  having  produced  the 
first  coal  mined  in  I'tah.  Coal  is  reported  to  have  heen  discovered  there  in  1857,  and  in  1SG2 
this  pioneer  coal  field  of  I'tah  was  opened.  In  the  early  seventies  a  railroad  was  constructed 
from  Nephi  to  Wales,  and  for  a  time  the  coal  was  taken  to  Salt  Lake  City.  The  Wales  coal  is 
of  interest  because  of  the  unusual  occurrence  of  t  he  deposit  immediately  between  two  beds  of 
limestone  of  Tertiary  age,  while  the  Sterling  coal  is  an  isolated  deposit  of  Laramie  (  '.)  age 
occurring  in  a  narrow-  fault   block. 
Sanpete  County  is  situated  in  the  centra]  pari  of  the  State,  in  the  plateau  country  immedi- 
ately southeast  of  the  termination  of  the  Wasatch  Ivange  at  Mount  N'ebo  (see  PI.  VIII). 
San  Pitch  River,  the  chief  northern  branch  of  the  Sevier,  occupies  a  broad  valley  in  the  center 
of  the  county.  The  mean  altitude  of  the  valley  is  about  5,200  feet ,  above  which  the  Wasatch 
Plateau  rises  6,000  feet  on  the  east ,  while  the  lower  ( in  unison  Plateau  limits  the  valley  on  the 
west.  Sanpete  County  lies  just  west  of  Carbon  County,  which  produces  most  of  the  coal 
mined  in  the  State. 
GENERAL   GEOLOGY. 
The  plateaus  of  this  pari  of  I'tah  are  underlain  chiefly  by  strata  of  Mesozoie  and  Tertiary 
age,  which,  except  along  lines  of  upheaval,  where  frequently  the  beds  are  sharply  tilted,  lie 
flat  or  only  gently  inclined.  The  rocks  containing  the  coals  are  of  Tertiary  and  Cretaceous 
age  and  the  valley  is  occupied  by  unconsolidated  Quaternary  deposits.  This  area  is  included 
in  the  map  of  the  Wheeler  Survey"  and  lies  immediately  north  of  the  region  studied  by 
Dutton.b 
Structure. — Sanpete  Valley  occupies  a  north-south  structural  trough,  which  separates  the 
Gunnison  and  Wasatch  plateaus.  On  the  western  side  of  the  valley  a  well-defined  fault 
extends  along  the  base  of  the  Gunnison  Plateau,  the  scarp  of  which  rises  abruptly  above  the 
valley,  exposing  cross-sections  of  low  ,  westward-dipping  Tertiary  strata.  Locally  the  pres- 
erve of  the  fault  is  accentuated  by  a  narrow  belt  of  Mesozoie  (?)  rocks  dipping  steeply  east- 
ward at  the  base  of  the  plateau.  On  the  east  a  monocline  of  large  proportions  is  well  devel- 
oped. The  rocks  at  the  summit  of  the  Wasatch  Plateau  lie  almost  flat,  but  toward  the 
western  rim  the  dip  is  low  to  the  west  and  along  the  flanks  increases  to  10°  or  15°,  con- 
stituting a  dip  slope  which  causes  the  strata  that  outcrop  on  the  summit  to  pass  beneath  the 
valley  filling.  The  monocline  is  broken  by  several  parallel,  north-south,  normal  faults  of 
small  dimensions.  South  of  Manti  other  and  larger  faults  are  developed  west  of  the  mono- 
cline.    The  Sterling  coal  lies  in  one  of  these  fault  blocks. 
oTJ.  S.  Geog.  Surv.  W.  100th  Mer.,  Atlas. 
&Dutton,  C.  E.,  ecology  of  the  High  Plateaus  of  Utah,  U.  S.  Geog.  and  Geol.  Surv.  Ilocky  Mt. 
Region,  1880. 
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